The present invention relates to non-emulsion additives for masonry cements. More particularly, the invention relates to a non-emulsion additive which, when used in masonry cements, provides masonry cement compositions having very low levels of air entrainment, while still possessing good workability and water retention.
Masonry cements are produced by intergrinding Portland cement (containing gypsum for proper setting time regulation), with, generally, from about 35 to 65%, based on the total weight, of a solid material such as limestone, chalk, talc, pozzolans, clay, gypsum, or combinations of such. Limestone is most often the ingredient interground with the Portland cement because of its low cost and good plasticity enhancing properties. Such masonry cements are ground to a greater degree of fineness than most Portland cements intended for use in structural concretes. The finer grind of masonry cements improves the plasticity of the finished mortar products.
Portland masonry cements ar compositions produced particularly for use by masons in the bonding of bricks, blocks and the like. Such cements are typically mixed prior to use with a fine aggregate, usually sand, and water. It is desirable that the wet mortar have a high degree of plasticity for working (e.g. troweling) by the mason, as well as other desirable properties such as good "board life" (i.e. a long working time), water-repellancy, etc. It is further desired that these cements possess good compressive strength, such that the structures built with the masonry cement will have good structural integrity.
The balance of workability vs. compressive strength which is obtained with a given masonry cement composition generally depends upon the level of entrained air in the cement composition. Masonry cements containing high levels of entrained air generally possess good workability and water retention, but relatively low compressive strength, while cements containing low levels of air generally possess good compressive strength, but are difficult for the mason to handle.
However, masonry cements having both low levels of entrained air, and hence good compressive strength, in combination with good workability can often be obtained by replacing some or all of the limestone component of the masonry cement with lime, a product obtained by heating naturally occuring limestone to form calcium oxide. However, masonry cement producers usually own, and are located at, limestone quarries, thus making limestone readily available and very inexpensive, whereas lime is generally costly, and must either be manufactured from the limestone by the cement producer or purchased from outside sources.
There is currently a trend in the industry toward implementing construction codes which would require lower levels of entrained air in masonry cements. If it is necessary to increase the level of lime used in masonry cements in order to meet these requirements the cost to the masonry cement producer will increase dramatically. Thus it would be very advantageous to producers of masonry cements to have an alternative, more economical method of reducing the air content in masonry cements, while retaining good workability.
Additive products are sold for mixture with masonry cements to enhance various properties of the cements, e.g. to improve the plasticity, water repellancy and set retardation of the masonry cement composition. It is common practice to mix such additive products with the cement during the intergrinding of the cement with the gypsum, limestone, etc.
In U.S. Pat. Nos. 3,865,601 and 3,885,985, the disclosures of which are incorporated herein by reference, additive products of the above type are described. The additives described therein comprise an aqueous oil-in-water emulsion containing water, a water insoluable, water-repelling acid component (e.g. tall oil, an emulsifier (e.g. a salt of such acid), and a setting time retarding agent (e.g. sucrose). This additive product is advantageously dispersible in water which reduces the risk of it being overdosed. The additive may also contain an air-entraining agent as an additional optional component.
An improved emulsion additive product is described in U.S. Pat. No. 4,375,987. In addition to the above-described constituents, this additive further comprises an emulsion stabilizer, (e.g. a glycol), which prevents the oil-in-water emulsion from destabilizing when exposed to freezing temperatures during shipping or storage prior to use.
The emulsion additive products described in the aforementioned patents have been successfully used to improve the water-repellancy, set-retardation, and plasticity of Portland masonry cements. However, in order to obtain optimal plasticity and workability and extended board life it is sometimes necessary to further add a water retention agent, such as a cellulose ether, during the grinding process. Such water retention agents generally entrain large quantities of air in the masonry cement, which, as described above, is undesirable in many applications. Furthermore, water retention agents cause the emulsion additives described above to destabilize and hence must be added as a separate feed stream, often as a dry powder. This method of addition is inconvenient and may increase the risk of overdosing the batch with the water retention agent.
Emulsion additives for masonry cements also have the disadvantage of often destabilizing (i.e. the emulsion "breaks") during storage. This may occur even when the additive contains a stabilizing component such as a glycol if the emulsion is exposed to severe temperature excursions or long-term thermal cycling. The destabilization generally occurs during storage or shipment of the emulsion, and usually renders the additive unusable.
Emulsion additives are also less economical to produce than a solution or suspension-type additive would be, as an additional manufacturing step is required to emulsify the additive.
Thus, it is desired to provide additives for masonry cements which, when interground with the cement, would produce a masonry cement having excellent workability and plasticity, in combination with an advantageously low air content and thus good compressive strength. It is further desired that these additives be provided as aqueous solutions rather than oil-in-water emulsions.